Topic 4 – Atomic Structure

• Dalton


  Tiny Spheres -uncharged -each element has its own sphere
• J.J Thompson


  Plum Pudding, Discovered e- can be removed from atoms, Positive sphere with random areas of negative charge (e-)
• Rutherford


  Nuclear model, Shot α at gold foil, Expected: α to pass with slight deflection, Observed: most passed through, some large deflection, Concluded: most of atom empty space, nucleus (+) centre

  
• Niels Bohr


  + Shells, Electrons orbit nucleus from fixed energy levels
• James Chadwick


  Discovered Neutrons
• Radioactive decay


  Unstable isotopes release radiation in order to stabilise
• Type Of Radiation


  • α = (2p + 2n) / He
  • β-= electron
  • γ = EM wave

  
• α


  • Strong, Weak, Stopped by Paper
• β-


  • Medium, Medium, Stopped by Aluminium
• γ


  • Weak, Strong, Stopped by Lead/Concrete
• Writing nuclear equations


  1. Gamma rays are also released sometimes as a side product

  2. New proton number = New element

  3. During (a) decay: 2P + 2N are released from nucleus

  4. During (b) decay: N -> P + e-

  5. Gamma decay does not change anything atomic/mass stay the same
• Nuclear processes


  • Alpha decay
  • Beta decay
• Half-life


  The amount of time it takes for half the radioactive nuclei to decay
• Count rate


  Measured in Becquerels (Bq) using a Geiger-Muller tube
• Short half life


  Faster decay = lots of radiation released = more dangerous
• START


  ÷ 2H = END
• Background radiation


  • Cosmic rays – solar radiation (PILOTS^ Risk)
  • Nuclear fallout/Nuclear waste
  • Radioactive rocks in mountains

  
• Radiation dose


  Your RISK of harm from radiation, affected by: Where you live and what job you do (pilots^, radiographer^ dose)

  
• IRRADIATION


  Object near but not touching radiation
• CONTAMINATION


  Radioactive atoms ON the object
• Avoiding radiation


  1. Lead boxes, Barriers, remote arms

  2. Wear suits, gloves, tongs

  3. Avoid Beta/Gamma outside body

  4. Avoid Alpha inside body
• Gamma sources


  • Medical Tracer (I123 – Thyroid gland)
• Gamma radiation


  Radioactive isotopes injected into patient, Gamma radiation released and penetrates out of the body from source, Followed by a detector
• Radiotherapy


  • Pros: Targeted to kill cancer cells
  • Cons: High doses – radiation sickness
• Nuclear fission


  Large nucleus absorbs neutron, Becomes unstable, Splits into smaller nuclei + neutron, Chain reaction
• Nuclear fusion


  Small nuclei join to create larger one, H + H = He, Lots of energy given out
• Nuclear fission


  Energy released as gamma rays: Heat water -> steam -> turbine
• Nuclear fusion


  More energy released than fission, But requires very high temp/pressure
• Controlling nuclear reactions


  Control rods absorb neutrons to control the rate of chain reaction
• Half Life


  The amount of time it takes for half the radioactive nuclei to decay